This invention relates generally to an apparatus for controlling a hydraulic circuit, and more particularly, to an apparatus for controlling the flow characteristics of an actuator.
Hydraulic drive systems are utilized in construction equipment such as hydraulic excavators, backhoe loaders, and end loaders. Known systems typically have a displacement controlled pump and one or more main flow control valves which are used to controllably actuate various hydraulic actuators associated with the vehicle. Normally, such drive systems are controlled through a series of operator control levers which are coupled to the control valves mechanically or hydraulically. The main control valve may include four independent valves which are used to control fluid flow from the pump to the actuator and to a tank or reservoir. Typically in this type of drive system the pump displacement changes much slower than the valve displacement. When the drive system shuts off, the valves in the main control valve shut off faster than the pump can destroke. This results in a volume of fluid or oil being trapped in the system which causes a large and sudden increase in the pump outlet pressure which can lead to undue wear on the pump.
Another contributor to the solution would be in the pump control. By adding the inverse of the current command to the command itself in the direction of command change, the response of the pump at startup and shutdown can be improved.
Accordingly, the present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the present invention a hydraulic control system has a pump for delivering fluid under pressure from a fluid reservoir, a hydraulic actuator selectively driven by the fluid, the system comprises a main flow control valve connected between the pump and the actuator for selectively providing the fluid to and from the actuator, and a control unit connected to the main flow control valve for controlling operation of the main flow control valve to control the rate of change of the area of the main flow control valve relative to the delivery of fluid from the pump. The control unit is also connected to the pump and controls displacement in response to either a flow command or in desired pressure.
In another aspect of the present invention a hydraulic control system having a pump for delivering fluid under pressure from a fluid reservoir, a hydraulic actuator selectively driven by the fluid, the system comprises a main flow control valve connected between the pump, the actuator, and the reservoir for selectively providing fluid to and from the actuator, the main flow control valve comprising four valves with each of the valves being selectively operated to further control the flow of fluid to and from the actuator, and a control unit connected to each of the valves and the pump which limits the rate of change of each of the valve areas separately, and which commands the pump flow based on the flow requested by the valves and rate of change of that request.